Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2002-12-20
2003-11-25
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S768000
Reexamination Certificate
active
06653736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of a multilayer flexible wiring board, and particularly to a multilayer flexible wiring board suited for mounting semiconductor elements.
2. Detailed Description of the Related Art
Recently, there is a demand to decrease semiconductor devices in size and a multilayer flexible wiring board which enables to mount bare chip semiconductor elements is regarded as important.
Now, referring to FIG.
8
(
a
), reference numerals
110
,
130
denote two kinds of flexible wiring board piece having a single layer structure. Fabricating steps of a multilayer flexible wiring board according to a conventional art will be explained by use of these flexible wiring board pieces
110
,
130
.
Out of the two kinds of flexible wiring board pieces
110
,
130
, one flexible wiring board piece
110
comprises a base film
112
, a metal wiring
115
arranged on the base film
112
, and a cover film
117
adhered on the metal wiring
115
.
The metal wiring
115
and cover film
117
are patterned in predetermined shapes, respectively. Thereby the cover film
117
has a plurality of openings
119
formed therein. Each of the openings
119
is positioned above the metal wiring
115
.
The other flexible wiring board piece
130
comprises a base film
137
, a metal wiring
135
arranged on the base film
137
, and a cover film
132
adhered on the metal wiring
135
.
The base film
137
, cover film
132
and metal wiring
135
are patterned in predetermined shapes, respectively. Thereby the cover film
132
and base film
137
have a plurality of openings
138
,
139
formed therein, respectively.
Each of the openings
138
,
139
is positioned above the metal wiring
135
. At the bottom of the opening
139
provided in the base film
137
, the surface of the metal wiring
135
is exposed. On the other hand, in the opening
138
provided in the cover film
132
, copper is filled by metal plating method. The copper is deposited to protrude from the cover film
132
surface and a solder coating
140
is formed at the tip thereof by metal plating method. As a result, a metal projection
142
is composed of a projection body
136
and the solder coating
140
.
To fabricate a multilayer flexible wiring board by adhering the above-mentioned flexible wiring board pieces
110
,
130
to each other, first, as shown in FIG.
8
(
a
), two flexible wiring board pieces
110
,
130
are positioned to face the cover films
117
,
132
thereof and a thermoplastic resin film
151
is interposed therebetween to close in contact with each other.
Upon heating, the thermoplastic resin film
151
is softened so as that an adhesive force thereof appears. Accordingly, when the flexible wiring board pieces
130
,
110
are pressed and heated to soften the thermoplastic resin film
151
, the cover films
117
,
132
are adhered to each other. At the same time, the metal projection
142
is forced in the softened thermoplastic resin film
151
, thereby the tip of metal projection
142
comes in contact on the metal wiring
115
(refer to FIG.
8
(
b
)).
In this state, a soldering metal composing the solder coating
140
is melted when the temperature of the flexible wiring board pieces
110
,
130
further increases. After cooling, the projection body
136
and the metal wiring
115
are connected with each other by the solidified solder metal
155
to obtain a multilayer flexible wiring board
150
(refer to FIG.
8
(
c
)).
When an electric part such as a semiconductor chip is connected with the flexible wiring board
150
, first they are appropriately positioned to each other. Next, as shown in FIG.
9
(
a
), a bump
175
formed on an element body
171
of an electric part
170
is positioned above the metal wiring
135
exposed at the bottom of the opening
139
in the base film
137
, and the tip of the bump
175
is allowed to come in contact onto the surface of the metal wiring
135
.
The bump
175
is composed of a projection body
172
including copper and a solder coating
173
formed thereon. When the electric part
170
is heated while the tip of the bump
175
is contacted with the metal wiring
135
, the solder coating
173
is melted to connect the projection body
172
with the metal wiring
135
.
Thus, the electric part
170
is connected with multilayer flexible wiring board
150
via solder coating
173
.
In the above-mentioned flexible wiring board
150
, however, the solder metal
155
within the flexible wiring board
150
is also heated when the solder coating
173
of the semiconductor chip
170
is melted.
In this case, connections deteriorate when the solder metal
155
becomes brittle or the solder metal
155
is re-melted. Reference numeral
156
in FIG.
9
(
b
) denotes a connecting portion between the metal wirings
115
,
135
within the flexible wiring board
150
. It shows that the solder metal
155
is re-melted and the connection between the metal wirings
115
,
135
worsens.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multilayer flexible wiring board in which the above-mentioned inconvenience does not occur and also to provide a fabricating method thereof.
In order to solve the above-mentioned problems, the present invention provides a fabricating method of a multilayer flexible wiring board, said method comprising the step of laminating a flexible wiring board piece having a metal wiring, in which a metal coating is exposed on at least a part of surface of said metal wiring, to another flexible wiring board piece having metal projections on the surface of which metal coating is formed, wherein one of or both of the surface of said metal coating formed on said metal wiring and on the surface of said metal projections is composed of a soft metal coating having a Vickers' hardness of 80 kgf/mm
2
or lower, and wherein the method further comprises the step of applying ultrasonic wave thereto in a state where said metal coating formed on said metal wiring contacts with the metal coating formed on the surface of said metal projections to connect said metal wiring with said metal projections.
Furthermore, the present invention provides a fabricating method of a multilayer flexible wiring board, said method comprising the step of adhering a flexible wiring board piece having a metal wiring, in which metal coating is exposed on at least a part of surface of said metal wiring, to another flexible wiring board piece having metal projections on the surface which metal coating is formed, wherein one of the metal coating formed on said metal wiring and the metal coating formed on the surface of said metal projections is composed of soft metal coating having a Vickers' hardness of 80 kgf/mm
2
or lower, the other one of the metal coating formed on said metal wiring and the metal coating formed on the surface of the metal projections is composed of hard metal coating having a Vickers' hardness of 120 kgf/mm
2
or higher and soft metal coating having a Vickers' hardness of 80 kgf/mm
2
or lower laminated on the said hard metal coating, and wherein the method further comprises the step of applying ultrasonic wave thereto in a state where the soft metal coating formed on said metal wiring contacts with the soft metal coating formed on said metal projections to connect said metal wiring with the metal projections.
Still further, the present invention provides the fabricating method of a multilayer flexible wiring board of the foregoing, wherein a thermoplastic film is interposed between said flexible wiring board pieces, adhering said flexible wiring board pieces to each other by said thermoplastic film in advance before applying ultrasonic wave thereto, and pressing at least one of said flexible wiring board pieces to contact the metal coatings with each other while applying ultrasonic wave.
Moreover, the present invention provides the fabricating method of a multilayer flexible wiring board in the foregoing, wherein at least one of said flexible wiring board
Hishinuma Hiroyuki
Kishimoto Soichiro
Oliff & Berridg,e PLC
Potter Roy
Sony Chemicals Corporation
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